1. Field of the Invention
The present invention relates to a method for crystallizing a solid material which is dissolved in water or an organic solvent. More particularly, the present invention relates to a process for preparing a crystallized solid or a concentrated slurry in high concentration by cooling a concentrated solution obtained from the evaporation of a solvent by employing a centrifugal thin film evaporator equipped with a heating section, cooling section and a scraper blade.
2. Description of the Prior Art
Heretofore, in order to crystallize a solid from a solution of the solid component in water or an organic solvent, usually the solvent is evaporated to concentrate the solution to a level greater than the solubility of the solid component in the solution or the solution is concentrated by evaporating all of the solvent.
For such operations, a centrifugal film evaporator equipped with a scraper blade (disclosed in Japanese Pat. Publication No. 9311/1960) is usually employed.
In this type of operation, if the melting point of the solid component is less than the evaporation temperature of the solvent or is near the evaporation temperature, for example, a solution of phthalic anhydride (melting point 131.8.degree.C) or maleic anhydride (melting point 52.6.degree.C) in benzene (boiling point 80.13.degree.C), or a solution of piperazine (melting point 106.degree.C) in methanol (boiling point 64.65.degree.C), the solid component in the concentrated solution resulting from the evaporation of the solvent is molten.
A need therefore continues to exist for a process and an apparatus by which a solid component having a melting point below or near the boiling point of the solvent from which it is crystallized can be obtained as a solid or a slurry and not as a molten material.